Binding of Fibrin Monomer and Heparin to Thrombin in a Ternary Complex Alters the Environment of the Thrombin Catalytic Site, Reduces Affinity for Hirudin, and Inhibits Cleavage of Fibrinogen
Interaction of the blood clotting proteinase, thrombin, with fibrin monomer and heparin to form a thrombin· fibrin monomer·heparin ternary complex is accompanied by a change in thrombin catalytic specificity. Equilibrium binding interactions in the assembly of the ternary complex were characterize...
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Published in | The Journal of biological chemistry Vol. 271; no. 42; pp. 26088 - 26095 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
United States
American Society for Biochemistry and Molecular Biology
18.10.1996
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Subjects | |
Online Access | Get full text |
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Summary: | Interaction of the blood clotting proteinase, thrombin, with fibrin monomer and heparin to form a thrombin· fibrin monomer·heparin
ternary complex is accompanied by a change in thrombin catalytic specificity. Equilibrium binding interactions in the assembly
of the ternary complex were characterized quantitatively using thrombin labeled at the active site with a fluorescent probe
and related to changes in thrombin specificity toward exosite I-dependent binding of hirudin and cleavage of fibrinogen. Changes
in the active site environment accompanying binding of heparin or fibrin to thrombin in binary complexes were reported by
fluorescence enhancements which contributed additively to the perturbation accompanying formation of the ternary complex.
Quantitative analysis of the interactions supports a preferentially ordered path of ternary complex assembly, in which initial
binding of heparin to thrombin facilitates binding of fibrin monomer with an ~40-fold increased affinity. Binding of fibrin
monomer in the ternary complex decreased the affinity of native thrombin for hirudin by >100-fold and inhibited cleavage of
fibrinogen, but this inhibition was overcome when fibrin(ogen)-fibrin interactions occurred. These results support a ternary
complex model in which heparin binding through exosite II of thrombin facilitates fibrin monomer binding via exosite I, with
accompanying changes in thrombin catalytic specificity resulting from perturbations in the active site and reduced accessibility
of exosite I to hirudin and fibrinogen. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0021-9258 1083-351X |
DOI: | 10.1074/jbc.271.42.26088 |